You can build a simple 555 timer circuit, and plug the capacitors in as the
timing cap. If the value is approximately right, then the cap is probably
ok.  This gets a little more complicated with higher voltage caps, since
they need to be re-formed after long storage without voltage.

For electrolytics, you may see a tolerance range of -20% to +50% or even
100%.
As caps age, they tend to decrease in value, I've seen them degrade to as
little as 1% of their nameplate value.
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